The present invention relates to a method and system for measuring and evaluating the temperatures in goods undergoing temperature processing such as heating or cooling processes. In particular, the present invention relates to such systems and methods as utilized in measurement and evaluation of the temperatures created in preserves during the sterilization process.
It is for example conventional in the food preservation technology to denote a so-called "sterilization value" which is indicative of the sterilization effect of a heating apparatus. Sterilization value F must be reached in order to keep the number of microorganisms within the food to a predetermined number. The desired sterilization value F varies as a function of temperature, the length of time a particular temperature is maintained, and the pH value of the goods. The following equation is applied: ##EQU1## T is the temperature at the critical location in the goods (also denoted as the core temperature) which is assumed to be maintained constant for a time interval .tau.. z is a number assigned to the pH value of the goods.
In practice, because of the cooling and heating portions of the cycle, the core temperature of the goods may not be considered constant. In this case the actual sterilization value L is taken as the sum of the partial sterilization values corresponding to sequential time intervals each having a time .DELTA.t. The total sterilization value is then calculated by the equation ##EQU2## The preserved food will be free of the excess microorganisms if, through a suitable heating process, it has been accomplished that L=F, that is it is necessary in order to control the sterilization that the actual sterilization value L is monitored continuously, that is the value of the sum in equation 2 is determined. In order to generate the sum it is of course necessary that the variation with respect to time of the temperature T be known. The calculation of this sum can be considerbly simplified by making some basic assumptions as to the temperature variation. Such simplifying assumptions for example may be: T is constant; T is a linear function or a logarithmic function of time. In the more general case in which T is not a simple function of time, it is usual to use the method of graphic analysis originated by Bigelow. For this, it is first necessary that an experimentally furnished curve of core temperature versus time be furnished. The temperature T during predetermined sequential time intervals is then derived from this curve and partial sterilization values .DELTA.L are computed. The sterilization value then results from the summing of the partial sterilization values, that is ##EQU3## Alternatively, the partial sterilization values .DELTA.L may be entered as ordinates plotted against suitable time values entered on the abscissa, the area under the curve then constituting the sterilization value L.
A number of errors are introduced by the various simplifying assumptions regarding the temperature variations as a function of time. All of the above-mentioned processes are time consuming and difficult and subject to many errors including calculating errors.